Vacuum pump with gas ballast device



July 3, 1962 A. LORENZ 3,042,292

VACUUM PUMP WITH GAS BALLAST DEVICE Filed May 22. 1959 2 Sheets-Sheet 1 22 124.5? W H W J II M: k w

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July 3, 1962 A. LORENZ 3,042,292

VACUUM PUMP WITH GAS BALLAST DEVICE Filed May 22, 1959 2 Sheets-Sheet 2 nited States 1.

3,042,292 Patented July 3, 1962 ice VACUUM PUMP WITH GAS BALLAST DEVICE Albert Lorenz, Hanan, Germany, assignor to W. C.

Heraeus G.m.bH., Hanan (Main) Germany, a corporation of Germany iled May 22, 1959, Ser. No. 815,194 Claims priority, application Germany May 30, 1958 3 Claims. (Cl. 230-207) The present invention relates to improvements in vacuum pumps, and more particularly to a vacuum pump which has at least one piston revolving eccentrically within a piston chamber and sealed therein by means of oil, and which is provided with a device for supplying secondary air or gas at certain times into the piston chamber.

It is a well-known fact that in the operation of vacuum pumps, normally liquid substances, especially Water, which are subjected to the suction of such a pump become vaporized, and thus enter the pump in the form of vapor or steam. In the subsequent compression of the evacuated air or gas, these substances again condense and contaminate the oil contained in the pump, thereby interfering with the proper operation of the pump. In order to remove these substances from the pump, a small amount of secondary air or gas, the so-called gas ballast, is fed into the pump shortly before the air or gas evacuated by it is discharged therefrom. This gas ballast is "at least partly taken along by the condensed substances when leaving the pump and it is thus sooner or later removed from the pump oil. However, since the pump conveys the air or gas continuously in the same direction from the suction side toward the pressure side, a considerable amount of lubricating and sealing oil is also discharged from the pump and has to be replenished to maintain the piston in a properly sealed condition.

Prior vacuum pumps of this type which were equipped with such gas ballast devices had a channel provided with a control valve which terminated into an end wall of the piston chamber. This had the considerable dis advantage that, during the operation of the pump, the oil penetrated continuously from the piston chamber into the gas ballast channel and had to be forced out therefrom by the newly injected ballast gas at every revolution of the pump piston. Since the end wall of the piston chamber was also continuously covered with an oil coating, an oil foam was formed at the point of entry of the gas ballast channel into the piston chamber, and this foam was at least partly taken along by the piston between its end surface and the end surface of the piston chamber and passed to the suction side of the latter. Consequently, the degree of efliciency of such a pump was seriously impaired by the gas ballast device and the degree of vacuum attainable was reduced considerably as soon as the gas ballast device was in operation. Although efforts have been made to overcome this deficiency by providing the gas ballast channel so as to terminate into the area between the piston chamber and the exhaust valve, this exhaust opening was also thickly coated with pump oil which then necessarily penetrated into the gas ballast channel and was again passed together with the ballast gas into the piston chamber and to the suction side thereof. Although the amount of air-saturated oil which was transferred by the piston to the suction side thereof was far less than in a vacuum pump of the type as first described, it was still considerable so that the final vacuum attainable by the pump was impaired when the pump was operated with a gas ballast.

The present invention is based upon a. proper recognition of the fact that the failure of all the previous vacuum pump designs operating with a gas ballast was due to the provision of a gas ballast inlet channel which communicated directly with the piston chamber by being connected to a bore in the wall of the pump housing which led directly into the piston chamber.

It is an object of the present invention to provide a vacuum pump operating with a gas ballast which completely overcomes the above-mentioned disadvantages.

A further object of the invention is to provide a vacuum pump with a special two-way valve which allows the air or gases conveyed by the pump to be discharged during the exhaust stroke of the pump piston and the gas ballast to be admitted into the piston chamber only as soon as the exhaust stroke is completed and when the pump piston begins its suction stroke.

The present invention therefore obviates the necessity of a special bore through the wall of the piston chamber to serve as an inlet of the gas ballast channel by pro viding an exhaust opening in the wall of the piston chamber which also forms the inlet opening of the gas ballast channel. The exhaust opening then leads to a valve disk which firmly closes the gas ballast channel during the period of the exhaust stroke of the pump piston and thus prevents any entry of oil from the piston chamher into the gas ballast channel at any time. On the other hand, as soon as the exhaust stroke of the pump piston is completed and the letter proceeds with its suction stroke, the ballast gas may freely pass through the valve into the piston chamben Such unrestricted entry of the ballast gas has the additional advantage that the vacuum pump according to the invention is capable of conveying a considerably greater amount of vapor or steam than could be conveyed by any of the known vacuum pumps with gas ballast devices. Furthermore, the reaction exerted by the gas ballast device according to the invention upon the suction side of the pump piston is considerably lower than the reaction exerted by the previous gas ballast devices.

The eflicient operation of the gas ballast control valve depends to a considerable extent upon providing its valve disk with a suitable spring of an initial tension which is just sufiicient to maintain the valve in the closed position when it is not actuated during the exhaust stroke of the piston. Thus, even a slight pressure above atmospheric within the piston chamber will be suficient to press the valve disk upon its seat so that no oil can enter into the gas ballast channel. 011 the other hand, even a slight under-pressure within the piston chamber will be sufficient to lift the valve disk off its seat on the mouth of the gas ballast channel so that the ballast gas can pass freely into the piston chamber.

Another feature of the present invention consists in combining the gas ballast control valve with the exhaust valve in such a manner that the control supporting shaft of the valve disks of the exhaust valve is secured to and extends entirely through the valve plate which forms the main body of the exhaust valve, and that this central supporting shaft is provided with a longitudinal bore so as to form a tubular member, the upper end of which is connected to the gas ballast channel proper, while the lower end forms the valve seat of the gas ballast valve.

In order to permit the entire two-way valve as well as the two individual valves thereof to be easily assembled, removed and exchanged, the invention further provides that the central supporting shaft, the lower end of which forms the seat of the valve disk of the gas ballast valve, is removably secured to the valve plate which forms the main body of the exhaust valve, and that the latter is also removably secured within the valve housing which may form an integral part of the wall of the piston chamber. The entire gas ballast device may then be installed or removed by inserting or removing the central supporting shaft. The removal of the supporting shaft is preferably carried out by first removing the entire exhaust valve body from the pump and by then unscrewing the supporting shaft therefrom. The valve disk of the gas ballast valve may also be very easily inserted or removed when the exhaust valve body is first removed.

The gas ballast channel leading to the outside of the pump is preferably provided with a branch conduit lead ing into an oil separator so that a part of the oil mist contained in the oil separating chamber will be drawn back into the piston chamber by the air or gas passing through the gas ballast channel. For regulating the amount of this sucked-up oil, the branch conduit may be provided with a control valve.

These and other objects, features, and advantages of the present invention will become further apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings of one preferred embodiment of the invention, in which-- FIGURE 1 shows a cross section of a vacuum pump with a gas ballast device according to the invention;

FIGURE 2 shows an enlarged cross-sectional detail view of the exhaust valve of the vacuum pump according to FIGURE 1; while FIGURE 3 shows a plan view of the valve disk of the exhaust valve for closing and opening the mouth of the gas ballast channel.

Referring to the drawings, the vacuum pump illustrated therein consists of a pump housing with a piston chamber 1 within which the rotary pump shaft 2 carries an eccentric 2a which is slidable within a piston 3 and thus adapted to revolve the latter within piston chamber 1 along and in engagement with the inner cylindrical surface thereof. Piston 3 is provided with a short intake or suction pipe 4 forming an intake channel 5 through which the intake chamber 6 communicates with the piston chamber 1 when the intake opening 7 of channel 5 is disposed below the rotary guide member 8.

According to the invention, piston chamber 1 is further provided with an exhaust channel 9 which leads through an exhaust valve 10 to the oil collecting and exhaust chamber 11 which is connected to an oil separator 12 in the form of a cyclone separator.

As illustrated more clearly in FIGURE 2, the exhaust valve 10 consists of a valve body 13 which may, for example, consist of a circular plate which is preferably removably secured within a recess in the wall of the pump housing and is provided with a plurality of bores 14 forming the exhaust channels from piston chamber 1. These exhaust channels 14 are adapted to be closed at their outer end by individual valve disks 15 which are connected to a supporting plate 16 by means of springs 17 which press valve disks 15 against the upper surface of plate 16 to close channels 14. Supporting plate 16 is rigidly secured to a short supporting shaft 13, for example, by being welded thereto. This supporting shaft 18 is centrally secured to valve body 13, preferably by being screwed into the same. According to the invention, shaft 18 has a longitudinal bore 19 and is removably connected by a sleeve 20 to a gas ballast conduit 21 which leads to the outside of the pump housing where it is connected to a control valve 22 for opening and closing the channel 21 and regulating the supply of air or gas, i.e. the gas ballast, into piston chamber 1. By means of a T joint 23, a branch pipe 24 leading into the cyclone separator 12 is connected to the gas ballast conduit 21 within chamber 11 and may also be provided with a suitable control valve 24a. This branch pipe 24 serves to conduct small quantities of air or gas from the separator 12 to the pump chamber 1 after initial start-up of the pump and when the ballast valve is closed. In normal operation, the ballast valve is closed after the water vapor in the system to be evacuated is substantially removed. Upon this occurrence, the valve 22 is closed allowing small quantities of air or gas to enter pump chamber 1 by way of conduit 24 from the separator 12. This air or gas serves to quiet the chattering of the valve 10 during operation of the pump and by being connected to the separator, the air or gas is scrubbed free of ambient dust and water vapor.

For closing bore 19 in shaft 18 and the gas ballast conduit 21 during the exhaust stroke of pump piston 3, the lower side of valve body 13 is provided with a valve disk 25 which is normally held under a slight pressure of a spring 26 in engagement with the lower annular end surface 27 of shaft 18 which projects slightly from the lower surface of valve body 13 and forms the valve seat for valve disk 25.

As illustrated in FIGURE 3, valve spring 26 preferably consists of a leaf spring with three radially projecting arms 26a, 26b, and 26c which extend at an angle of to each other and rests on a surface 28 within a chamber 29.

It will be evident from the foregoing description that an entry of oil from piston chamber 1 into bore 19 in supporting shaft 18 and conduit 21 is absolutely prevented by valve disk 25 in cooperation with spring 26 and the valve seat 27 on the lower end surface of supporting shaft 18.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no way limited to the details of such embodiment, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully described my invention, what 1 claim is:

1. In a vacuum pump having a housing, at least one piston chamber within said housing, a piston eccentrically revolvable in said piston chamber and oil-sealed therein, a suction chamber intermittently communicable with said piston chamber, said piston chamber having an exhaust opening, an exhaust chamber connected to said exhaust opening, an exhaust valve adapted to close said exhaust opening toward said exhaust chamber during the suction stroke of said piston, conduit means for intermittently passing a gaseous medium from the outside of said pump into said piston chamber, said conduit means passing through said exhaust chamber and being connected substantially centrally to said exhaust valve, the end of said conduit means passing through said exhaust valve and facing toward said exhaust opening of said piston chamber forming a valve seat, a valve disk adapted to engage with said valve seat to close said conduit means during the exhaust stroke of said piston, leaf spring means for holding said valve disk under a very slight pressure in engagement with said valve seat when said valve disk is not being actuated by said gaseous medium passing from the outside of said pump through said conduit means.

2. In a vacuum pump having a housing, at least one piston chamber within said housing, a piston eccentrically revolvable in said piston chamber and oil-sealed therein, a suction chamber intermittently communicable with said piston chamber, said piston chamber having an exhaust opening, an exhaust chamber connected to said exhaust opening, an exhaust valve adapted to close said exhaust opening toward said exhaust chamber during the suction stroke of said piston, conduit means for intermittently passing a gaseous medium from the outside of said pump into said piston chamber, said conduit means passing through said exhaust chamber and being connected substantially centrally to said exhaust valve, said exhaust valve including a valve body being formed with channels therethrough extending from the side facing toward said exhaust opening toward the side facing toward said exhaust chamber, said valve body having a central aperture, a tubular shaftlike member mounted on said valve body within said aperture, means for connecting the free end of said tubular member to said conduit means, a supporting member mounted on said tubular member, a plurality of exhaust valve disks resiliently mounted on said supporting member and being adapted during the suction stroke of said piston to close said channels in said valve body, a valve disk adapted to close said central aperture in said valve body at the side facing toward said exhaust opening during the exhaust stroke of said piston, and spring means for holding said valve disk under a very slight pressure in engagement with said valve body when said valve disk is not being actuated by said gaseous medium passing from the outside of said pump through said conduit means and said tubular member.

3. In a vacuum pump having a housing, at least one piston chamber Within said housing, a piston eccentrically revolving in said piston chamber and oil-sealed therein, a suction chamber intermittently communicable with said piston chamber, said piston chamber having an exhaust opening, an exhaust chamber connected to said exhaust opening, an exhaust valve adapted to close said exhaust opening toward said exhaust chamber during the suction stroke of said piston, conduit means for intermittently passing a gaseous medium from the outside of said pump into said piston chamber, said conduit means passing through said exhaust chamber and being connected substantially centrally to said exhaust valve, said exhaust valve including a valve body being formed with channels therethrough extending from the side facing toward said exhaust opening toward the side facing toward said ex- 6 haust chamber, said valve body having a central aperture, a tubular shaftlike member mounted on said valv body within said aperture, means for connecting the free end of said tubular member to said conduit means, a supporting member mounted on said tubular member, a plurality of exhaust valve disks resiliently mounted on said supporting member and being adapted during the suction stroke of said piston to close said channels in said valve body, a valve disk adapted to close said central aperture in said valve body at the side facing toward said exhaust opening during the exhaust stroke of said piston, and spring means for holding said valve disk under a very slight pressure in engagement with said valve body when said valve disk is not being actuated by said gaseous medium passing from the outside of said pump through said conduit means and said tubular member, the annular end surface of said tubular member facing toward said exhaust opening and slightly projecting from said valve body forming a valve seal adapted to be closed by said valve disk.

References Cited in the file of this patent UNITED STATES PATENTS 1,650,494 Dally et al Nov. 22, 1927 2,191,345 Gaede Feb. 20, 1940 2,196,287 Baudette Apr. 9, 1940 2,779,533 Ziock Jan. 29, 1957 

